The invention relates to a pulverizing installation comprising a ball mill including a rotary drum having a horizontal axis and each end of which comprises a journal resting on a bearing, the mill being fed with material to be pulverized and with gas via at least one of its ends by means of a feed device comprising a feed pipe for feeding with material to be pulverized, a rigid gas injector tube passing axially through the corresponding journal, said rigid tube and said journal defining therebetween an annular duct, said feed pipe discharging into said annular duct in the vicinity of the corresponding journal, said journal containing a rigid helicoidal Archimedes screw structure disposed about said rigid gas injector tube, said rigid helicoidal structure turning with the drum when it drum rotates in order to feed the material to be pulverized towards the interior of the rotary drum, an outlet duct communicating with said annular duct for ejecting the mixture constituted by the gas and by the material pulverized in the form of powder out of the drum.
Such installations are used in particular to pulverize solid fuels to feed them in pulverized form to the burners of boilers. The balls, or equivalent other pulverizing members, which are made from a hard material, pulverize the material by crushing, grinding, and/or attrition. The material is introduced into the rotary drum in the form of particles of varying coarseness via the journals which support the drum at its ends. The pulverized material is carried out of the drum by means of a gas. The gas is introduced into the drum of the ball mill via the journals at the same time as the material to be pulverized and follows a circuit enabling it to leave the drum. The gas used is generally air. It is fed into the drum either via one of the journals, leaving via the other journal charged with the powder material, or symmetrically via each of the two journals, through which it also exits in a contraflow configuration with the pulverized material by virtue of the presence of deflector members.
If the material to be pulverized is damp, the injected gas is heated. It then dries the pulverized material it conveys. The pulverized material generally has a relatively wide range of particle sizes and it is known in the art to pass it through a separator which lets through only the fine grains of the material and recycles the coarse grains back into the drum.
Document U.S. Pat. No. 2,285,429 describes a pulverizing installation as defined above. In the installation described, the gas for conveying the pulverized material is fed in through a journal by means of a hollow tube carrying the Archimedes screw and coaxial with and inside the journal. The hollow tube is fixed by a system of bars to the interior of the drum of the ball mill and rotates on its axis with the drum. As a result, at least some parts of the system of bars are subject to the impact of the moving balls as the drum turns. The hollow tube is supported by a bearing which must be sealed against the dust conveyed by the charged gas and it must be continuously cooled if the gas has previously been heated for the purpose of drying the material.
The installation in a journal of the drum of a tube fixed to the drum and to an end bearing does not facilitate access to the parts of the ball mill subject to wear, in particular the balls, the Archimedes screw and the bars supporting the hollow tube. It is then necessary to demount other parts of the ball mill to obtain access to the above parts that are subject to wear, a particular consequence of which is to increase the maintenance and down times of the ball mill.
The object of the present invention is to mitigate those drawbacks and to propose a pulverizing installation as defined above, the installation being characterized in that said feed pipe for feeding material to be pulverized is substantially vertical and discharges into said annular duct at the level of a guide member for directing the material to be pulverized as conveyed by the pipe towards the drum, in that said rigid gas injector tube is held immobile and penetrates into the journal by passing through said guide member from the outside, and in that said rigid helicoidal structure is fixed to the journal.
The injector tube axially introduced into the journal at one end of the drum is mounted on an immobilizing frame which can be moved relative to the drum.